Heart failure can cause lethargy, but it is also typically associated with certain physical exam findings (heart murmur, enlarged liver, swollen feet, distended neck veins). If her lethargy and poor appetite persist, though, she should be re-evaluated. A few things to note include whether she is losing weight, any easy bruising or bleeding, if she gets tired or short of breath on exertion or at night, and if her bowel patterns have changed. It would be reasonable for her to have some basic lab work—including thyroid tests and checking for anemia—to look for a cause of her fatigue and poor appetite that could be easily corrected. Even mild anemia can cause significant fatigue in an older person, so you should consider whether she’s getting an adequate amount of dietary iron and folate. Another common cause of poor appetite is depression.